Screwworm Update

Diana Barto

Sun, 2001-04-01 12:00

A new diagnostic kit may help reinforce screwworm eradication efforts in the U.S. and beyond. What has orange eyes, bluish-green body and might try to invade the U.S.? The culprit is no alien from outer space. It's the screwworm fly and its larvae the screwworm. This parasite nearly devastated the livestock industry in the southern U.S. in the 1900s. The USDA has eradicated screwworm from the U.S.,

A new diagnostic kit may help reinforce screwworm eradication efforts in the U.S. and beyond.

What has orange eyes, bluish-green body and might try to invade the U.S.?

The culprit is no alien from outer space. It's the screwworm fly and its larvae — the screwworm. This parasite nearly devastated the livestock industry in the southern U.S. in the 1900s.

The USDA has eradicated screwworm from the U.S., but trade and travel to and from screwworm-infested regions like South America make re-infestation a concern for U.S. livestock producers.

The screwworm enters open wounds and feeds on the flesh of livestock and other warm-blooded animals. If left untreated, a screwworm-infested wound is deadly. Multiple infestations can kill a grown steer in five to seven days, according to the USDA's Animal and Plant Health Inspection Service.

Identifying and containing screwworm flies trying to sneak back into the U.S. isn't easy. Differentiating screwworm fly maggots from similar fly species currently requires visual examination in a lab and takes several days.

But, a new diagnostic field kit may speed up the identification and containment of these pests, says Steve Skoda, Agricultural Research Service (ARS) Midwest Livestock Insects Research Unit, Lincoln, NE. Developed by Skoda and other ARS scientists, the test allows a veterinarian to confirm a suspected screwworm in just six hours.

Because response to a suspected screwworm outbreak could include coordinating costly sterile fly releases, speed and accuracy are critical to choosing and applying the appropriate responses, Skoda says.

The kit is 99.9% accurate, and the test area turns blue when a specimen is a screwworm. Its accuracy hinges on an antibody that binds with a protein antigen in screwworm tissue samples. Skoda's lab and University of Nebraska graduate James Lester Figarola discovered the protein.

Agdia Inc., Elkhart, IN, is collaborating with ARS to commercialize the technology and says a commercial test kit could be available to U.S. veterinarians within two years.

The company estimates it will cost $5-20/sample, depending on the number of tests performed at one time, says Willye Bryan, insect diagnostics manager for AgDia. The kit will be available for purchase through the AgDia product catalog.

In the U.S., Skoda says, the kit will be used primarily as a tool to prevent the reintroduction of screwworms on live animals at ports of entry.

Besides providing a way to quickly identify cases that need treatment, use of the kit in other countries will help export officials detect early cases of screwworm in animals intended for export. It will also assist in case identification in trouble spots of the eradication program, Skoda says.

Screwworm also has been eradicated in Mexico and as far south as the Costa Rica/Panama border in Central America. Eradication efforts are underway in Panama and the Caribbean, but South America currently has no plans to begin eradication.

Screwworm eradication — including regulation of cattle movement, wound treatment and the release of sterile flies — benefits the U.S. livestock industry more than $900 million a year, according to USDA.